Fyzikální ústav Akademie věd ČR

Seminar Friday, 19/04/2013 14:00 - 15:00

Speakers: M. Etzkorn (Max Planck Institute for Solid State Research, Stuttgart, Germany)
Place: Na Slovance, main lecture hall
Presented in English
Organisers: Department of Condensed Matter Theory

Abstract: Scanning tunnelling microscopy (STM) is well known for its capability to characterize and manipulate structures on the atomic scale. We have improved the time resolution of STM into the nanosecond regime employing well defined time pattern on the applied bias voltage [1]. Using an all electronic pump-probe scheme we follow the relaxation of a spin excitation in a single Fe-Cu-dimer. With a first higher amplitude pump-pulse, we drive the spin system into the excited state and then use a small amplitude probe-pulse to read out the spin state at a defined time delay. As visible in the figure an exponential dependence of the recovery of the tunnelling current on the pump-probe delay is found that can be understood on the basis of a single rate limiting relaxation process. The observed relaxation times strongly depend on external magnetic fields and reach about 200 ns. The experimental data proofs that the relaxation is due to tunnelling of magnetization. We have recently extended the above mentioned all electronic scheme by also detecting the photons emitted from the tunnel junction. With the help of the photon emission one can directly map the transient bias profile of the voltage applied at the tunnel junction. This knowledge can be used to optimize the bias pulses applied. The introduced methods present a general approach to extent the time resolution of STM to the nanosecond regime and below without major modifications of existing setups.

[1] S. Loth, M. Etzkorn, C.P. Lutz, D.M. Eigler, and A.J. Heinrich, Science 329 (2010) 1628.

Time dependence of the tunneling current that results from the spin relaxation of a Fe-Cu dimer on Cu2N. For magnetic sensitivity a Mn-atom was placed on the STM tip apex. The measurements have been preformed at a temperature of 0.6 K and a magnetic field of 7 T.